This invention relates to the emulsification and colloidal stabilization of emulsions and dispersions of hydrophobic in aqueous phases using a coacervate emulsifying or dispersing agent, and particularly to the coacervate emulsification or dispersion of non-rosin sizing agents. The invention is also directed to a stable sizing composition stabilized by the coacervate, a method of making the stable sizing composition, a method of using the sizing composition to produce sized paper, and sized paper, including paperboard, sized with the sizing composition.
Although the coacervate of the present invention may be useful for stabilizing various diverse types of emulsions and dispersions, including mineral oil in water, the invention will be described with reference to its preferred use as a stable emulsifying or dispersing agent for sizing agents for paper, and particularly, non-rosin sizing agents.
While there are a myriad of details for manufacturing paper, the paper manufacturing process conventionally comprises the following steps: (1) forming an aqueous suspension of cellulosic fibers, commonly known as pulp; (2) adding various processing and paper enhancing materials, such as strengthening and/or sizing materials; (3) sheeting and drying the fibers to form a desired cellulosic web; and (4) post-treating the web to provide various desired characteristics to the resulting paper, including surface application of sizing materials, and the like.
Sizing agents are typically in the form of aqueous solutions, dispersions, emulsions or suspensions which render the paper treated with the sizing agent, namely sized paper, resistant to the penetration or wetting by an aqueous liquid, including other treatment additives, printing inks, and the like. Sizing agents are internal additives employed during papermaking or external, surface additives employed at the size press that provide the enhanced characteristics.
Many different types of nonreactive and reactive sizing agents are well known in the papermaking industry. Paper typically made under acidic paper making conditions, referred to as acid paper, is usually sized with well-known rosin-derived sizing agents (referred to herein as "rosin sizing agents"), which are generally considered to be nonreactive sizing agents. Some papers made under neutral and alkaline paper making conditions may also be sized with rosin sizing agents. The above-identified related applications disclose coacervate dispersing agents for rosin sizing agents. The present invention is directed primarily to coacervate dispersing and emulsifying agents for non-rosin sizing agents typically used to make paper under alkaline paper making conditions, referred to as alkaline paper, as well as for general use in making stable dispersions and emulsions of other generally immiscible oil and aqueous phase compositions. The coacervate stabilizing agent of this invention is also usefull in stabilizing emulsions and dispersions of mixtures of sizing agents, including reactive and non-reactive, rosin and non-rosin sizing agents.
The most common sizing agents for fine alkaline paper, are alkenyl succinic anhydride (ASA) and alkyl ketene dimer (AKD). Another class of sizing agents useful for sizing fine paper includes ketene dimers and multimers that are liquid at room temperature, such as alkenyl ketene dimers and multimers. These are reactive sizing agents, since they have a reactive functional group that covalently bonds to cellulose fiber in the paper that causes their hydrophobic tails to be are oriented away from the fiber. The nature and orientation of these hydrophobic tails cause the fiber to repel water.
Certain properties of sizing agents are important to control for their efficient and economical use in making paper. One important property is sizing efficiency, i.e., the degree of sizing obtained per unit of sizing agent added. Sizing efficiency is determined by the amount and cost of materials used in making the sizing agent to obtain a desired sizing characteristic or group of characteristics. A more efficient sizing agent results in the desired characteristics at a lower amount or a greater efficiency, and thus, improved papermaking economies. Excess sizing agent can result in significant decreases in the paper quality by creating deposits on the papermaking machine, causing defects in the paper. Such deposits also reduce the production rate.
Sizing characteristics are affected by the type of sizing agent used, the type of paper to which the sizing agent is applied, and many other factors which have been the subject of a great deal of work in the past and a continuing body of work presently by those in the paper treatment industry. The present invention relates to sizing agent compositions in the form of emulsions or dispersions, cationic colloidal coacervate dispersion compositions for non-rosin sizing agents and mixtures of non-rosin and rosin sizing agents, as well as methods of making and using the resulting compositions and dispersions. The term "emulsion" (liquid in liquid) is sometimes used in the paper making industry to refer to what is technically a "dispersion" (solid in liquid).
Most sizing dispersions are made by a process involving forming an emulsion of a hydrophobic sizing agent in an aqueous medium at a temperature at which the sizing agent is in a liquid form. Upon cooling to ambient temperature the emulsion droplets solidify and a sizing dispersion results. The process needs an emulsifier and a stabilizer in order to process well. Upon application to the wet end of the paper making process, the particles of the sizing agent adsorb onto the cellulose fiber. Thermal drying causes the positioned sizing particles to melt and distribute along the fiber. The fiber then becomes less wetting, i.e. sized.
Polymers have been used in the past to help with the emulsification and also to promote interaction of the sizing particles with cellulose fiber suspensions. Starches and water soluble polymers such as polyamidoamines have been used in this context.
Various sizing compositions comprising sizing agents and dispersion aids have been previously disclosed.
International Application Publication No. WO 97/28311, published Aug. 7, 1997, corresponds to copending parent U.S. application Ser. No. 08/594,612 and now-abandoned grandparent U.S. application Ser. No. 09/046,019, of which the present application is a continuation-in-part, as noted above. The published International Application discloses a coacervate of the type used in the present invention used as an emulsifier system for rosin sizing agents. There is no disclosure of the use of the coacervate for emulsifying, dispersing or stabilizing other types of sizing agents or other hydrophobic/aqueous systems.
U.S. Pat. No. 4,240,935 (Dumas) discloses a paper sizing composition comprising a ketene dimer, an anionic dispersing agent such as sodium lignin sulfonate, certain water-soluble cationic resins and water. The cationic resins are composed of the reaction products of epichlorohydrin and an aminopolyamide derived from a dicarboxylic acid and a polyalkylene polyamine having two primary amino groups and at least one secondary or tertiary amine group. Another group of cationic resins is the reaction product of epichlorohydrin and the condensates of cyanamides or dicyandiamnide with a polyalkylene polyamine having a given formula including such compounds as polyethylene polyamines, polypropylene polyamines and polybutylene polyamines.
U.S. Pat. No. 4,263,182 (Aldrich) and U.S. Pat. No. 4,374,673 (Aldrich) both disclose aqueous paper sizing compositions in the form of dispersions consisting essentially of finely divided fortified rosin particles, a water-soluble or water-dispersible cationic starch dispersing agent for the rosin particles, an anionic surface-active agent and water. The distinguishing characteristics between the patents include the use of different types of starches. The '182 patent discloses using cationized starches which are anionic starches modified by reaction with one of five groups of cationizing resin, or a starch modified by reaction with a water-soluble polyamine resin containing epoxy groups. The '673 patent uses cationic starches made by reacting starch with compounds containing both amine groups and groups reactive with hydroxyl groups of the starch, where the reaction involves formation of covalent bonds. Various emulsification and dispersion-forming steps are disclosed involving the particular cationic starch dispersing agents.
U.S. Pat. No. 4,657,946 (Rende et al) discloses paper sizing compositions comprising alkenyl succinic anhydride sizing agents in an emulsion including cationic water-soluble vinyl addition polymers and surfactants which may be anionic, non-ionic or cationic where one of the cationic emulsifiers can be poly(diallyldimethylammonium chloride).
U.S. Pat. No. 4,861,376 (Edwards et al.) discloses stable, high solids dispersions of ketene dimer using water-soluble carboxylic acid with cationic starch, sodium lignin sulfonate and aluminum sulfate. In some instances, commercial embodiments include the post addition of poly(diallyldimethylammonium chloride), as a promoter, rather than in the emulsification system.
U.S. Pat. No. 5,318,669 (Dasgupta) and U.S. Pat. No. 5,338,407 (Dasgupta) disclose a process and composition for enhancing the dry strength of paper without substantially reducing the paper's softness. Added to a bleached pulp furnish, separately or together, are an anionic polymer and a cationic polymer. The anionic polymer may be various guar materials and carboxymethyl bean gum. The cationic polymer may be other types of cationic guar and bean gums, cationic acrylamide copolymers and resins based on reactions of various polymers with epichlorobydrin.
U.S. Pat. No. 5,338,406 (Smith) discloses a composition and method for enhancing the dry strength of paper made from pulp of unbleached fibers, and especially those containing black liquor. The composition comprises a polyelectrolyte complex comprising at least one water-soluble, linear, high molecular weight, low charge density cationic polymer having an indicated reduced specific viscosity and charge density, and at least one water-soluble, anionic polymer having a charge density less than 5 meq/g. The cationic polymer may include synthetic polymers such as copolymers of acrylamide, including copolymers of acrylamide with diallyldimethylammonium chloride. Anionic components may include those normally present in unbleached pulps, such as solubilized lignins and hemicelluloses, synthetic anionic polymers and anionically modified natural polymers. Sodium lignin sulfonate is mentioned as an example of an effective anion.
U.S. Pat. No. 5,393,337 (Nakamura et al.) discloses a rosin emulsion sizing agent for papermaking comprising a fortified or unfortified rosin-epoxy compound obtained by reacting a rosin and an epoxy compound. The rosin-epoxy compound is dispersed in water with the aid of an emulsifying and dispersing agent. The emulsifying and dispersing agent can be various kinds of low-molecular weight surfactants, polymer surfactants and protective colloids such as casein, polyvinyl alcohol, or modified starch, used singly or in combination.
Despite the efforts of the industry to develop cost-effective, efficient and stable paper sizing dispersions and emulsions having the appropriate desired properties, there are still many problems that have been encountered. Many polymers which are used to make sizing dispersions have limitations. On one hand, if the molecular weight is too small, no final stabilization is possible because the steric effects are not there. On the other hand, if the molecular weight is high enough for a good steric effect, then ionic contamination can cause particle bridging and ensuing Theological problems during storage. In many cases, as in the use of naturally derived polymers such as starches, the molecular weight is not easily controllable and these hydrocolloids have limited use because of their great tendency to bridge. Sizing dispersions must be kept at low solids contents to prevent high rheological properties.
This invention uses a coacervate concept. Two oppositely charged polymers are mixed in such a proportion to produce a third system, a cationic colloidal coacervate, which functions as an emulsifier or dispersant and stabilizes the emulsified or dispersed sizing agents. Using this technique, the particle charge, which plays an important role in particle deposition on cellulose fiber, can be more precisely controlled, by controlling the ratio of the oppositely charged polymers making up the coacervate. The highly charged particles provide for better retention of the size in the pulp. Non-rosin coacervate-stabilized sizing agents of the present invention have enhanced sizing efficiency and are stable over anticipated periods of use and storage.
As used herein, the term "non-rosin sizing agent" means any sizing agent capable of sizing cellulosic pulp products, such as paper and paperboard, which does not include rosin as a component of the sizing agent, except if rosin or a rosin sizing agent is specifically indicated as being included in a mixture with a non-rosin sizing agent. Illustrative categories of materials that are non-rosin sizing agents, and examples of specific types of sizing agents will be set forth hereinafter.
This invention encompasses coacervated systems which can be used to emulsify, disperse and stabilize sizing emulsions and dispersions, as well as emulsions and dispersions including simple oils, such as mineral oil, and various aqueous phases, most simply including water. In general, these systems comprise a mixture of an anionic and a cationic polyeletrolyte, which, when mixed properly, yield an insoluble colloidal coacervate. This colloidal coacervate is then available for adsorption at the liquid/liquid interface of the molten or naturally liquid sizing agent and water. Upon proper adsorption and shear, emulsification of the sizing agent into the aqueous dispersion medium can occur and the result can be two-fold: If the sizing agent, such as an AKD, is a solid at room temperature, then cooling the emulsion results in a stable solid in liquid dispersion. If the sizing agent is a liquid at room temperature, as in the case with certain alkenyl ketene dimers or multimers, then the process results in and stays as an emulsion. The coacervate adsorbs as a multitude of soft gelatinous particles, thereby increasing the viscosity at the interface and yielding stability of a different kind. In many cases, the individual components of the coacervate would not produce a stable dispersion or emulsion when used by themselves or when added to the sizing agent or other composition to be stabilized. The charge on the particle can be controlled by controlling the ratio of the polyelectrolytes that make up the coacervate. Some schools of thought may desire to rename these coacervates as polyelectrolyte complexes. These two concepts are the same, one being from the colloidal school and the other from the polymer school of thought. Each polyelectrolyte does not have to be soluble. One can be colloidal and the other soluble. Because no true surfactants (i.e.: micelle forming) need to be used, these sizing systems can be more hydrophobic and can also be of larger particle size.
Since the coacervate of the present invention acts as both a dispersing agent to disperse solid components in liquid and an emulsifier to emulsify immiscible liquids, resulting in stable dispersions and emulsions, respectively, the coacervate of the present invention will be referred to hereinafter as a "coacervate stabilizing agent."
The disclosures of all of the patents, patent applications and other publications identified anywhere herein are hereby incorporated herein by reference.